Cardiac arrythmias, and atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. In patients with normal sinus rhythm, the heart, which is comprised of atrial, ventricular, and excitatory conduction tissue, is electrically excited to beat in a synchronous, patterned fashion. In patients with cardiac arrythmias, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue as in patients with normal sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction has been previously known to occur at various regions of the heart, such as, for example, in the region of the sino-atrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmias, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self propagating. Alternatively, or in addition to the multiwavelet reenetrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion.
A host of clinical conditions may result from the irregular cardiac function and resulting hemodynamic abnormalities associated with atrial fibrillation, including stroke, heart failure, and other thromboembolic events. In fact, atrial fibrillation is believed to be a significant cause of cerebral stroke, wherein the abnormal hemodynamics in the left atrium caused by the fibrillatory wall motion precipitate the formation of thrombus within the atrial chamber. A thromboembolism is ultimately dislodged into the left ventricle, which thereafter pumps the embolism into the cerebral circulation where a stroke results. Accordingly, numerous procedures for treating atrial arrhythmias have been developed, including pharmacological, surgical, and catheter ablation procedures.
Catheter ablation procedures treat atrial fibrillation through cardiac tissue ablation. Examples of catheter-based devices and treatment methods have generally targeted atrial segmentation with ablation catheter devices and methods adapted to form linear or curvilinear lesions in the wall tissue which defines the atrial chambers, such as those disclosed in U.S. Pat. No. 5,617,854 to Munsif, U.S. Pat. No. 4,898,591 to Jang, et al., U.S. Pat. No. 5,487,385 to Avitall, and U.S. Pat. No. 5,582,609 to Swanson, the disclosures of which are incorporated herein by reference. The use of particular guiding sheath designs for use in ablation procedures in both the right and left atrial chambers are disclosed in U.S. Pat. Nos. 5,427,119, 5,497,774, 5,564,440 and 5,575,766 to Swartz et al., the entire disclosures of which are incorporated herein by reference. In addition, various energy delivery modalities have been disclosed for forming such atrial wall lesions, and include use of microwave, laser and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall, as disclosed in WO 93/20767 to Stern, et al., U.S. Pat. No. 5,104,393 to Isner, et al. and U.S. Pat. No. 5,575,766 to Swartz, et al., respectively, the entire disclosures of which are incorporated herein by reference.
The success of catheter based ablation procedures has led to numerous improvements to the catheters used for the procedures. However, the traumatic nature of the ablation procedure has given rise to certain complications. One such complication is the possibility of damaging the esophagus, which lies very close to, and often touches the outer wall of the left atrium. Damage to the esophagus is sometimes caused when the esophagus touches or is close to the tissue in the left atrium that is being ablated. The heat from the ablation procedure may penetrate through the tissue of the left atrium and reach the esophagus. This damage to the esophagus is extremely dangerous, as the damaged esophagus often becomes infected. The damage to the esophagus often manifests as a fistula, or hole, that develops over time. This hole causes any infection to spread to the heart wall. This damage carries an extremely high mortality rate. Accordingly, a need exists for a device that provides a protective shield and a physical barrier between the esophagus and the heart during ablation procedures.